The present invention relates to a damping material which has a high damping effect, especially, which has a wide operating temperature range and which has excellent adhesion strength and adhesive followability. The damping material of the present invention is mainly used for vehicles, vessels, electric and machine appliances, and building materials.
As is well known, damping materials are used in various fields in order to prevent and suppress the vibration and the noise which are caused due to the rotation of an engine, a motor or the like which is incorporated into vehicles such as automobiles and electric cars, vessels, and electric and machine appliances such as washing machines, drying machines, acoustic apparatuses, precision machine tools, and factory and plant machines and tools; to prevent and suppress the vibration and the noise generated in the water or gas conduits or air-conditioning ducts in office buildings and houses; and to prevent the vibration caused by vehicles running on the road or railroad tracks.
With the recent tendency of lightening and/or miniaturizing the vehicles, vessels, electric and machine appliances and building materials, the damping materials used therefor have also been required to be lightened, thinned and miniaturized. For this purpose, a damping material is strongly required to have a high damping effect (for example, the peak value of the loss factor .eta. is not less than 0.30).
In addition, since damping materials are often used under the circumstance of the wide temperature range, it is further desirable that a high damping effect can be maintained in as wide a temperature range as possible, in other words, that an operating temperature range is wide (for example, the width of the operating temperature range of the loss factor .eta. of not less than 0.3 is at least 20.degree. C.).
A damping material is also required both to fully display a high damping effect when mounted on a base material and to have an excellent operability such as easiness to handle and mount on the base material. For this purpose, a damping material is strongly required to have an excellent adhesion with the base material, in other words, to have an excellent adhesive strength (e.g., not less than 30 kg/cm.sup.2), and to closely and conformingly adhere to the base material, in other words, to have an excellent adhesive followability (e.g., not more than 2 mm) which enables the damping material to sufficiently closely-conformingly adhere to the base material while adapting it to the rough surface or the complicated shape of the base material.
A damping material is generally produced by molding a filler such as mica powder and a binder into a sheet form or block form by extrusion-molding, calendering, compression-molding, injection-molding, cast-molding or the like. A damping material is most frequently used in the sheet form together with a base material such as a steel plate to which the damping material is attached by fusion-bonding or adhesion. As a method of enhancing the damping effect of a damping material, a method of thickening the damping material and a method of adding a large amount of filler having a high density so as to increase the weight of the damping material are well known. By these methods, however, it is difficult to lighten, thin and miniaturize a damping material as described above. As a countermeasure, investigations of methods of enhancing the damping effect by adjusting the composition and the mixing ratio by varying the kinds of the filler and the binder, and the mixing ratio thereof have recently been carried out. For example, the applicant of the present invention has proposed the following vehicle damping sheet in Japanese Patent Application Laid-Open (KOKAI) No. 2-302455 (1990) (corresponding to European Patent No. 0383580A).
"A vehicle damping sheet comprising a blend-mixture comprising: (1) a filler composed of mica, iron oxide particles and an auxiliary filler; and (2) a binder composed of an ethylene-vinyl acetate copolymer,
each of the amounts of the mica, the iron oxide particles and the auxiliary filler being 5 to 200 parts by weight per 100 parts by weight of the binder; the total amount of the mica, the iron oxide particles and the auxiliary filler being not less than 30 parts by weight per 100 parts by weight of the binder; and the content of the iron oxide particles in said blend-mixture being from 2 to 40% by weight."
Further, Japanese KOKAI 2-302455 discloses that as the auxiliary filler, calcium carbonate, clay, talc, barium sulfate, asbestos, silica balloon, fibrous material such as waste paper, chemical fiber and wood fiber, etc. may be exemplified and they are used alone or as a mixture thereof, and in particular, the fibrous material such as waste paper, chemical fiber or wood fiber can reduce the flow property of the damping sheet when it is thermally fused to the floor panel of an automobile, thereby preventing disconnection or sagging.
Also, Japanese KOKAI 2-302455 discloses Example 6 that to a binder of 40 parts by weight of ethylene-vinyl acetate copolymer and 60 parts by weight of petroleum resin, a filler of 20 parts by weight of Fe.sub.3 O.sub.4 particles (size: 0.3 .mu.m) as the iron oxide particles, 90 parts by weight of mica (size: 150 .mu.m), 25 parts by weight of calcium carbonate, 10 parts by weight of waste paper and 10 parts by weight of a process oil was added and blended, and after mixing under heating the blend in a dispersion mixer at a temperature of 120 .degree. to 140.degree. C. for 10 min., the thus obtained blend-mixture was rolled spread by a calender rolls to prepare a vehicle damping sheet of 2 mm in thickness.
The applicant of the present invention has also proposed the following damping materials in International Application No. PCT/JP92/00534.
"A self-fusion type damping material comprising: hard ferrite particles as a filler; and a binder,
the binder being composed of an ethylene-vinyl acetate copolymer and a petroleum resin which are mixed with the filler so that the amount of the filler is 150 to 600 parts by weight based on 100 parts by weight of the total amount of the ethylene-vinyl acetate copolymer and petroleum resin." and
"A self-fusion type damping material comprising: as a filler hard ferrite particles which are mixed with an auxiliary filler selected from scaly powder such as mica and plate-like iron oxide particles, a ballooning agent such as glass and silica, calcium carbonate, clay, barium sulfate and zinc oxide; and a binder,
The binder being an ethylene-vinyl acetate copolymer and a petroleum resin which are mixed with the filler so that the amount of the hard ferrite particles is 50 to 400 parts by weight based on 100 parts by weight of the total amount of the ethylene-vinyl acetate copolymer and petroleum resin and the amount of the auxiliary filler is 1 to 200 parts by weight based on 100 parts by weight of the total amount of the ethylene-vinyl acetate copolymer and petroleum resin, and that the total amount of the filler and the auxiliary filler is 100 to 600 parts by weight based on 100 parts by weight of the total amount of the binder."
Although a damping material having a high damping effect, and excellent adhesion strength and adhesive followability is now in the strongest demand, the damping sheet disclosed in Japanese Patent Application Laid-Open (KOKAI) No. 2-302455 (1990) cannot be said to have either a sufficiently high damping effect or a wide operating temperature range because the width of the temperature range thereof in which the loss factor .eta. is not less than 0.3 is at most 18.degree. C. In addition, the adhesive strength and the adhesive followability of the damping material disclosed in Japanese KOKAI 2-302455 are about 28 kg/cm.sup.2 and about 2 to 3 mm, respectively, which cannot be said to be satisfactory.
As a result of studies undertaken by the present inventors so as to solve the above-described technical problems, it has been found that by mixing and blending 30 to 180 parts by weight of a filler composed of scaly powder with 100 parts by weight of a binder composed of an ethylene-vinyl acetate copolymer containing 30 to 65 wt % of vinyl acetate and a petroleum resin mainly containing an aromatic petroleum resin, wherein the amount of petroleum resin is 160 to 330 parts by weight based on 100 parts by weight of the ethylene-vinyl acetate copolymer, the produced damping material has a high damping effect and excellent adhesion strength and adhesive followability. On the basis of this finding, the present invention has been achieved.